Froth flotation of phosphate values involving ph control



June 29, 1954 w. A. HODGES ETAL 2,682,337

FROTH FLOTATION OF PHOSPHATE VALUES INVOLVING PH CONTROL Filed Dec. 29,1950 zz/q Josepk E F/ogd Patented June 29, 1954 FRO'ILH FLOTATION 0FPHOSPHATE VALUES INVOER/HN@ pH CONTROL William A. Hodges, Plant City,and Joseph E. Floyd, Fort Meade, Fla., assignors to Swift & Company,Chicago, Ill., a corporation of Illinois Application December 29, 1950,Serial No. 203,454

2 Claims. (Cl. 209-166) The present invention relates generally to aprocess for concentrating phosphate ore by selective flotationseparation, and more particularly to a process for concentratingphosphate ore wherein pH control is employed to produce a high gradephosphate concentrate.

Phosphate ores have been concentrated by several general methods, themost practical of which comprises treating the ore with reagents adaptedto selectively iioat the phosphate particles of the ore upon suitableagitation.

The principal object of the present invention is to provide an improvedprocess for the selective otation of phosphatic material wherein greateryields are obtained.

A further object of the present invention is to provide a process forphosphate flotation involving pH control of the flotation conditions.

Additional objects if not specifically set forth herein will be readilyapparent to one skilled in the art from the following detaileddescription of the invention.

In the drawings:

Fig. l represents a flow sheet for the method of the present invention,showing in diagrammatical form the steps followed in carrying out theinvention.

The present invention, in general, comprises the steps oipreconditioning deslilned phosphatic feed, subjecting the conditionedfeed to a frothflotation operation, repulping the froth so obtained andrefloating to recover a high grade phosphate concentrate.

More specifically, it has been found that if the pI-I values in thevarious steps are controlled within certain specific limits, therecovery of phoshate is markedly increased. These critical pl-l limitsin thD various steps are as follows:

In the pre-conditioning cells, 8.5-9.0 pli;

in the flota-dion cells (initial), 7.8-8.2 pH; and

In the reflotation cells (nal) 6.4-6.8 pl-I.

For example, the phosphatic feed, deslimed by decantation or anyconventional method, is first conditioned at approximately 70 per centsolids for about 2 minutes. In carrying out this step, the deslimed feedtogether with sufficient water to make a pulp of about 70 per centsolids content is introduced into a mister, horizontal or vertical,together with an alkali, fatty acid, and an unsaponiiiable oil, whichare added in sufficient quantities as to cause a selective coating cithe phosphate particles. The pH of the conditioning cells is maintained,by correct proportioning oi' the alkali added, within the range 8.6-9.0.The conditioned feed is then passed to i.'

a bank of flotation cells maintained at a pH oi 7.8-8.2, where it isagitated and aerated to produce a froth. This froth, which contains afairly high percentage of phosphate together with some silica, is thenrepulped with water and refloated, without using further reagents, inthe second bank of flotation cells maintained at a pH of 5.4-6.8. Themiddlings obtained in this second bank of cells be returned to theconditioning cells to be reworked with new feed ior the purpose ofrecovering additional B. P. L. values. The froth removed from the secondbank of flotation cells will be found to have, as a general rule, about90 per cent or better of the B. P. l... present in the original feed.

Referring now to the drawing of Fig. l, the deslimed phosphatic feedfrom a classifier it is passed into a suitable mixer or conditioningcell l i wherein it is throughly mixed and conditioned with water fedinto the mixer through line I2 and an alkali-fatty acid-unsaponifiableoil mixture fed in through line I3. The amount of alkali added isregulated so as to maintain a pH of 8.6-9.0 in the conditioning cell.After about 2 minutes from the time that the reagents are added, theconditioned pulp is introduced through line it together with water fromline l5 into a dotation machine or bank of rougher cells le. In thesecells the pulp is aerated and agitated causing air bubbles to attach togroups of phosphatic particles. These aerated phosphate groups rise tothe surface where they are removed as a froth and introduced into asecond bank of flotation cells known as cleaner cells il through lineIt. The siliceous gangue or tailings pass out of the bottom of therougher cells to waste through line l5). The pl-l of the rougher cellsis maintained at '7.8-8.2 by the addition of water of the necessary pHthrough line l5. In the cleaner cells the phosphate concentrate in thefroth from the rougher cells is reoated by the addition of water throughlines 20 and again aerated and agitated in the same manner as in therougher cells. The pH of the cleaner cells is held at 6.4-6.8 by theaddition through line 20 of the necessary quantity of acid, prei-Verably sulfuric acid. This operation causes some of the siliceousparticles entrapped in the initial otation froth from cells iii to bereleased and sink to the bottom of the cells Il whence they are removedtogether with a small amount of phosphatic particles as middlingsthrough line 2i. Those middlings can be recirculated through the entireflotation process as indicated in Fig. 1 to recover additional phosphatevalues.

The enriched froth obtained in the refloating process in cells il' isremoved by paddles and is pumped directly to storage through line t2.The lower pli oi' acts as a depressing agent for the entrapped silicaparticles and also causes the phosphate particles to be floated more orless as individual particles which is not the case in the initialflotation stage or rougher cells wherein a higher pli. is maintained.

The following specic examples are included for the purpose ofillustration only, and are not to be construed as limitations on theinvention claimed herein:

Example I For the purpose of illustration, in this and followingexamples, the conditioning cells will be referred to as the conditionercell; the first flotation cell as the rougher cell and the secondflotation cell as the cleaner cell.

A B (pH of (pH of cleaner cleaner cell, 7.9) cell, 6.5)

pH of conditioner cell 8. 9 9.0 pH ci' rougher cell 8.0 7.8 Poundsreagent/ton feed:

NaOH 0. 30 0.30 Fatty Acid.. 0. 43 0.43 ucl O' 1. 29 1. 29 conditioningtime (rn 2 2 time in rougher cell (sec 32 32 time in cleaner' cell(sec.) 34 37 Percent concentrates 39, 4 33.6 3. 1 8.8 57. 5 57.6 31. 4931.09 73. 63 76.69 15. 35 42.99 3. 49 2. 6l 5. 62 3. 00 o\ ed roughercell., 93. 62 95. 16 Percent B. P. L. recovered in final product. 92. 1282. 98 Percent B. P. L. recovered by reworklng middlings 93. 51 93.05Percent SiO in rougher concentrate eliminated in cleaner cell 52.2 79. 5

Example II In the following example, the pH of the cleaner cell under Awas held at '7.6; and the pH of the cleaner cell under B was held at6.6.

(Middlings could be reworked to recover additional B. P. L. values.

Example III Under A, cleaner cell pH was held at 7.8.

Under B, cleaner cell pH was held at 6.6. Under 0, cleaner cell pH washeld at 6.4.

A B C pH of conditioner cell...

pH of rougher cell Pounds reagents/ton fee Percent concentrates...Percent middlmgs Percent tailmgs..

B. P. L. Tailings..- SiO Concentrates Percent B. P. L. in Feed l0Percent B. P. L. in Concentrates... Percent B. P. L. in MiddlingsPercent B. P. L. in Tailings Time in rougher cell (see.) 3 Time incleaner cell (sec.) 3

The above examples illustrate that a higher B. P. L. content is found inthe recovered phosphate when the pH of the cleaner cell is lowered. Thisresults in a somewhat higher percentage of middlings, which however maybe reworked to recover additional B. P. L. values. The pH values for theconditioning, flotation, and reflotation steps are critical and must becarefully maintained in order to obtain the increased recovery ofphosphate values made possible by the present invention. In theconditioning and initial flotation steps a higher pH than the rangespecied results in a large quantity of foam formation with attendantflotation of undesirable silica. In these steps a pH below the specifiedrange results in a depressing action which causes the excessive loss ofphosphate values in the tailings. In the cleaner cells or reilotationstep, a pH above the critical range specified results in a lower gradeof recovered phosphate concentrates, while a lower pH than specifiedresults in prohibitive loss of phosphate values in the middlings.

The particular collecting agent does not form part of the presentinvention and any suitable agents may be substituted for the fattyacid-fuel oil-NaOH mixture illustrated herein. For example, instead ofNaOH, the alkali used may be potassium hydroxide, ammonium hydroxide,anhydrous ammonia, and less preferably, the hydroxides of calcium,barium, and lithium. Oleic and linoleic acids are the best fatty acidreagents, but other unsaturated fatty acids can be used successfully.All fatty oil acids such as cottonseed, palm, peanut, soyabean, sh, talloil, etc., can be used. Also, soaps made from these fatty acids andsulphonated fatty acids and sulphonated petroleums can be used. Fuel oilhaving a gravity of 20 Baum is preferred, although lighter or heavierpetroleum oils can be used. Unsaponifable fatty oils can also be used.

The term deslimed phosphatic feed as used in the appended claims isintended to cover a mixture of deslimed ore and water forming a pulp ofsuitable consistency for handling in the conditioning cells, preferablyas aforesaid comprising about a 70 per cent solids content.

Obviously, many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof and, therefore, only such limitations should beimposed as are indicated in the appended claims.

We claim:

1. A process for the froth flotation of phosphate values from deslimedphosphatic ore which comprises: intimately mixing with deslimedphosphatic feed a mixture of reagents comprising an alkali, a fatty acidand an unsaponiable oil at a pH within the range of 8.6-9.0; passing theresulting mixture of deslimed feed and reagents into an agitating zonemaintained at a pH within the range of '7.8-8.2 whereby aphosphate-bearing froth is formed; repulping said froth with water andrefrothing at a pH within the range of 6.4-6.8 to produce a frothcontaining substantially all recoverable phosphate.

2. A process for the froth-flotation of phosphate values from deslimedphosphatic ore which comprises: conditioning deslimed phosphatic feedwith a mixture of an alkali, a fatty acid and an unsaponiable oil at apH of from 8.6-9.0; frothing the resulting mixture in an agitating zoneat a pI-I of from 7.8-8.2 to form a phosphatebearing froth; separatingout the froth so formed and repulping at a pH Within the range of6.4-6.8; and refrothing the mixture at this pH to oat substantially al1recoverable phosphate in the form of a high phosphate-contentconcentrate.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,293,640 Crago Aug. 18, 1942 2,461,813 Duke Feb. 15, 1949Number Milling 6 FOREIGN PATENTS Country Date Great Britain Apr. 22,1941 Great Britain Dec. 20, 1948 OTHER REFERENCES Methods for 1934,published by the A. I. M. M. E., New York, N. Y., 1935, pages 452 and460. 0

(Copy in Div. 25.)

1. A PROCESS FOR THE FROTH FLOTATION OF PHOSPHATE VALUES FROM DESLIMEDPHOSPHATIC ORE WHICH COMPRISIES: INTIMATELY MIXING WITH DESLIMEDPHOSPHATIC FEED TO A MIXTURE OF REAGENTS COMPRISING AN ALKALI, A FATTYACID AND AN UNSAPONIFIABLE OIL AT A PH WITHIN THE RANGE OF 8.6-9.0;PASSING THE RESULTING MIXTURE OF DESLIMED FEED AND REAGENTS INTO ANAGITATING ZONE MAINTAINED AT A PH WITHIN THE RANGE OF 7.8-8.2 WHEREBY APHOSPHATE-BEARING FROTH IS FORMED; REPULPING SAID FROTH WITH WATER ANDREFROTHING AT A PH WITHIN THE RANGE OF 6.4-6.8 TO PRODUCE A FROTHCONTAINING SUBSTANTIALLY ALL RECOVERABLE PHOSPHATE.